Antenna



Dec. 6, 1960 R. YATES ETAL 2,963,704

ANTENNA Filed Jan. 20, 1955 LESTER R. YATES CHARLES MERVYN DORSEY, JR.FINLEY H. WELDON INVEN TOR.

7 ATTOR S United States Patent O ANTENNA Lester Raymond Yates, CharlesMervyn Dorsey, Jr., and Finley Houston Weldon, Baltimore, Md., assignorsto The Bendix Corporation, a corporation of Delaware Filed Jan. 20,1955, Ser- No. 483,022 1 Claim. (Cl. 343895) This invention relates toradio antennas and more particularly to an antenna especially adapted toairborne installations.

Antennas for such service are subject to conflicting requirements. Inmodern high speed aircraft, protruding members must be kept to a minimumlength and be adaptable to an air-foil shape in order to minimize drag.On the other hand, the strength of the radiated field increases withantenna length and reduction in length is in many cases not compatiblewith field strength requirements.

Furthermore, such antennas intended for use in communications must beable to function effectively over a wide range of frequencies. Theantenna impedance must remain matched over this range of frequencies tomaintain a low standing wave voltage ratio.

Lightning also is a problem and it is desirable that provision be madefor a direct path to ground for direct current without impairing theoperating qualities of the antenna and with a minimum of added expense.

It is an object of this invention to provide an antenna having a lengthwhich is of small fraction of the operating wave length and capable offunctioning efficiently over a wide band of frequencies, exhibiting alow standing wave voltage ratio over the whole range.

It is a further object of the invention to provide such an antenna whichis easy and inexpensive to build.

It is another object of the invention to provide an antenna having abase loading circuit so arranged that it includes a direct path toground for direct current flowing in the antenna, thus constituting aneffective protective device against lightning without the addition ofadditional structure for that purpose.

It is an additional object of the invention to provide a verticallypolarized antenna capable of being given a swept-back form foraerodynamical reasons without introducing any appreciable pickup of thehorizontal signal component.

The above and other objects and advantages of the invention are realizedby an antenna comprising a thin ribbon of conductive material wound inthe form of a spiral about a form having a flattened helicalcross-section. The antenna is overcoupled to a base mounted antiresonantcircuit.

The invention will be further explained with reference to theaccompanying drawing, in which:

Fig. 1 is a view in elevation of an antenna embodying the invention;

Fig. 2 is a plan view of the form of anti-resonant circuit utilized inthe embodiment of Fig. 1;

Fig. 3 is a cross-section view of the antenna of Fig. 1, taken along theline 33; and

Fig. 4 is a schematic diagram of the antenna and base loading circuit ofFig. 1.

Referring now to the drawing, there is shown in Fig. 1 a mast shapedform mounted on a base plate 11 which may be a portion of the skin of anaircraft. The form 10 may be made of any suitable dielectric materialhaving the necessary strength, such as Bakelite or any of variousavailable moldable plastic compositions. The cross-sectional shape ofthe mast is that of a flattened oval as shown in Fig. 3, and the mastmay be raked 7 back from the vertical as shown in Fig. 1, to providegood aerodynamical characteristics.

Wound around the mast in the form of a helix is a thin ribbon conductor12. The ends of the ribbon are secured to the form as indicated at 13and 14 by any desired conventional fastener, such as a screw. Thehelical conductor is the radiating element of the antenna.

The antenna is completed by an anti-resonant circuit, mounted on thebase 11, to which the helical element 12 is overcoupled. Theanti-resonant circuit is preferably composed of a hair-pin type inductor15, illustrated in Figs. 1 and 2, having its ends slotted, as at 16, andhaving a fixed capacitor 17 conductively secured between its ends. Thelower end of the radiating element 12 is connected to an intermediatepoint of the inductor 15 by a conductor 18. The antenna is fed by meansof a coaxial transmission line 20, the outer conductor of which isconnected to the base plate 11 which acts as ground and the innerconductor of which is connected to an intermediate point of the inductor15 by means of a conductor 19. The slots 16 in the ends of the inductorpro vide for its adjustment by movement of the capacitor therealong.

In the operation of the antenna the distributed loading of the flattenedhelix brings it to resonance at the middle of the frequency range towhich the ant=i-resonant circuit is tuned. The latter circuit transformsand parallel compensates the impedance of the radiating element toproduce a low standing wave ratio.

In an embodiment of the invention constructed for use in the frequencyrange extending from 118 to 132 me. the mast was fourteen inches long,three and a half inches wide, and one half inch thick at its thickestpoint. The radiating element was a ribbon of copper one half inch wideconnected by the anti-resonant circuit to a fifty ohm transmission line.With this construction the standing wave ratio did not exceed 1.8 at anypoint within the range. The horizontal component of the signal wasnegligible.

The mast and radiating element may be covered with a coating ofdielectric material if desired, or an aerodynamically shaped housing ofsimilar material may be placed over it.

It should be noted that lightning protection is built into theconstruction by virtue of the direct conductive path from the radiatingelement 12 through the upper end of the coil 15 as shown in Fig. 4 andthence to ground 11.

What is claimed is:

An antenna comprising an elongated form of dielectric material having across-section shaped in the form of a flattened oval, a conductiveribbon wound upon said form in a helix, means for mounting said formwith a base end adjacent a ground plane and projecting from said groundplane with one end of said ribbon adjacent and the other end remote fromsaid ground plane, a U- shaped inductor at said base end having opposedslots in the free ends of said U-shape and a connection to said groundplane from a point on one side of said U-shape, a capacitor of magnitudeto resonate said inductor at signal frequency selectively positioned insaid slots, a two conductor transmission line having one conductorconnected to said ground plane, and the other conductor connected tosaid inductor, and a direct connection between said inductor and saidone end of said ribbon, said connections to said inductor being atspaced points remote from the terminals of said capacitor.

References Cited in the file of this patent UNITED STATES PATENTS2,081,274 Hahnemann May 25, 1937 2,575,377 Wohl Nov. 13, 1945 2,652,492Shanklin Sept. 15, 1953

